Nickel base alloy and article



United States Patent 3,383,206 NICKEL BASE ALLOY AND ARTICLE Stanley T.Wlodek, Bethel Park, Pa., assignor to General Electric Company, acorporation of New York No Drawing. Continuation-impart of applicationSer. No.

333,619, Dec. 26, 1963, now Patent No. 3,304,176, dated Feb. 14, 1967.This application Oct. 11, 1965, Ser. No. 494,966

5 Claims. (Cl. 75-171) This is a continuation-in-part of applicationSer. No. 333,619, filed Dec. 26, 1963, now Patent No. 3,304,176.

This invention relates to nickel base alloys and, more particularly, toa solid solution type nickel base alloy of improved dynamic oxidationresistance.

In copending application Ser. No. 333,619, filed Dec. 26, 19 63 andassigned to the assignee of this invention there is described a nickelbase alloy of improved oxidation resistance and fabrica-bility resultingfrom the addition of about 0.05 to less than 0.3 weight percent La to aNi-Cr-Fe type nickel base alloy solution strengthened with either orboth Mo and W.

The alloy of the copending application provides an unexpectedimprovement in oxidation resistance over similar known alloys. Thisimprovement is now seen to be significant when used in a relativelystatic application such as in a furnace. However, it has been recognizedthat such an alloy requires further improvement for use under dynamicoxidation conditions. One example of a use under dynamic conditions isas a combustor material in a gas turbine engine where there is a rapidflow of combustion gases including excess oxygen.

A principal object of the present invention is to provide an alloy ofthe type described in the above identified c0- pending application buthaving improved oxidation resistance under dynamic oxidation conditionsas well as under static oxidation conditions.

Another object is to provide such an alloy which, under dynamicoxidation conditions, will form an improved surface as a thermalreaction product in an oxidizing atmosphere to resist further oxidationof the alloy and to act as a barrier to internal oxidation.

Still another object is to provide an article including such an alloyand having an oxidation resistant surface.

These and other objects and advantages will be more readily recognizedfrom the following detailed description and examples. These are intendedto be exemplary of rather than any limitation on the scope of theinvention.

It has been found that the above objects can be accomplished bycombining lanthanum with certain spinel formers in the type of alloydescribed.

Briefly, the present invention provides an improved nickel base alloy ofthe solution strengthened type from which an improved article can beproduced, the alloy consisting essentially of, by weight, 20-23% Cr;8-10% Mo; 17-20% Fe; up to 0.15% C; up to 2% W; 0.05 to less than 0.3%La; 0.56% of the spinel forming elements selected from the group Co andMn, the Co when selected being in the range of 13% and the Mn whenselected 3,383,206 Patented May 14, 1968 being in the range of 0.53%with the balance nickel and incidental impurities.

In a preferred form, the alloy of the present invention includesO.1-0.2% La along with 1.5-2.5 Co and 0.5- 1.5% Mn.

During further evaluation of the alloy of the above identifiedco-pendiug application and its comparison with the alloy claimed in US.Patent 2,703,277, Spendelow et al., it was recognized that much of theadvantage in oxidation resistance which resulted from the addition ofthe specified amount of lanthanum was lost during oxidation in highvelocity combustion products. Consideration of the mechanism throughwhich the lanthanum addition is effective indicated that unlike theknown alloy of the above identified United States patent where-in themain reaction or surtace products were Cr O and spinel (NiCr O thereaction or surface products of the lanthanum modified alloy of thecopending application consisted only of Cr O Although this rhombohedralsurface scale was very protective under static exposure conditions, theabsence of spinel overgrowths above the Cr O layer resulted in chromiumvolatilization in high velocity environments. This led to chromiumdepletion and an increased oxidation rate under such conditions.

As a result of understanding this mechanism, it was recognized that thecontrol and definite inclusion of certain levels of strong spinelformers such as Mn and Co could provide an alloy having a combination ofimproved oxidation resistance under both static and dynamic conditions.However, other spinel formers such as iron already included in the alloyhad little, if any, eliect on the reaction products.

The spinel formers manganese and cobalt were identified as impurities inthe composition of the alloy of the copending application and of thealloy of the Spendelow et al. patent. They were not specificallyincluded nor were their amounts controlled. In the Spendelow et a1.patent, cobalt is included as an impurity generally at less than 1% andin no event greater than about 2.5%; manganese is listed as an impuritypermissible up to about 1% along with silicon and the like.

It has been recognized that when certain spinel formers such as Mn andCo are specifically controlled within the range of 0.5-6% for the totalof such elements, a different kind of alloy surface is formed as anoxidation reaction product during and retained after both static anddynamic oxidation. Such a surface reaction product is different fromthat formed in either of the known alloys, and is highly stabilized. Itsspinel portion is of the form Ni(Cr, Mn, Co) O rather than merely theNiCr O of the known alloys. The following Table I lists the types ofsurfaces found with each of the prior alloys and of the alloy of thepresent invention both under static and dynamic conditions. Example A isthe alloy listed in US. 2,703,277, Example B is one form of the alloy ofthe copending application and Example 1 is the preferred form of thealloy of the present invention because of its relative ease ofreduction. The compositions for these examples are found in Table II.

TABLE I.SURFACE COMPARISON AFTER 1,000 HRS. AT 2,000 F.

E Static Oxidation Dynamic Oxidation Outer Surface Subsurface OuterSurface Subsurface A CnO; plus Spinal A SiOz plus Spinel A Splnel A SiOlus S lnel A. B (Cr, LahOs do i3 2). p 1 (Cr, La)z0a plus Splnel B (Cr,La)z0s plus Spine] B- O4. Spinal B =N 1(Cr, Mn, C0)204;

TABLE II [Weight Percent-Balance Ni] Example Cr Mo Fe O W La Co Mn Si l.2 17. 7 0. 10 0. 65 1. 0. 5 0. 9 9. (5 18. 3 0. 0.33 0. 09 0 0 0. 3 218. 5 0. 00 0. 04 0.17 1. 9 1.0 0. 8 8. G 18. G 0. 09 0. 43 0. 05 2. 42.8 O. 8 S. 5 18. 2 0. 10 0. 30 O. 17 3. 0 5 0. 8

These alloys were melted in a 100 pound vacuum induction furnace. The 1%Mn variation shown as Example 1 in Table II was successfully reduced tosheet and subjected to extensive oxidation evaluation and somemechanical testing.

As was mentioned above, the alloy of the copending application, shown inthe tables by Example B has signii'icantly improved oxidation resistanceunder static conditions over the known alloy, represented by Example A.The following Table III gives a comparison of Examples A and B with eachother and with the preferred form of the alloy of the present invention,represented by Example 1, under static oxidation resistance.

TABLE III-AVERAGE STATIC OXIDATION TESTING l Spalling of surfacereaction products occurred on cooling. 2 A ditional 2 mils/side of lineuniformly distributed internal oxide also oserved.

While Example B has oxidation resistance under static conditions betterthan does Example 1, the alloy of the present invention shown as Example1 in Table III has static oxidation resistance at least equal to that ofExample A. Although Example A experienced a lower weight gain at 2000 F.after 400 and 1000 hours static exposure, nevertheless, the reactionproduct surface of Example A spalled upon cooling. The surface ofExamples B and 1 did not. The effectiveness of the reaction productsurface to prevent internal oxidation is significantly greater in AlloysB and 1. Thus the alloy of the present invention has good oxidationresistance under static conditions, in general better than that ofExample A.

The most significant difference between the alloy of the presentinvention and the other listed alloys is in dynamic oxidationresistance. Whereas the alloy of Example 13 is better under staticoxidation conditions, it has significantly lower resistance in dynamicoxidation testing. This is shown more particularly in the data of TablesIV and V.

shown by the data of Table V. With regard to potential dimensionalchange of articles made from the alloy of Example 1 and after dynamiccyclic thermal experience, it is interesting to note that the alloy ofExample 1 ex- 5 perienced no loss in width as a result of formation ofits improved surface.

TABLE V.DYNA.\1IC OXIDATION TESTING IN FLAME TU N'EL [Average after1,000 hours] 10 Avg. Depth Internal Oxi- Avg. width Example Temp, F.dation (mils/side) loss (m)i1s/ side Front Rear Thus the alloy of thepresent invention particularly represented by Example 1 is characterizedby a combination of good static oxidation resistance and significantlybetter dynamic oxidation resistance.

The dynamic oxidation testing was conducted as thermal cyclicevaluations performed on 2.0" x 0.375" specimens.

The surface of all specimens to be used for oxidation testing wereprepared by mechanical abrasion up to and including 600 grit paper.Final surface preparation consisted of vapor blasting the surface of thespecimen using 1250 grit abrasive.

The specimens were supported in one end of a flame tunnel in afire-brick with the majority of the specimen exposed to an uninterruptedgas/air flow of about 100 lbs./in. /hr. The tests were performed bycycling from 20 minutes at temperature followed by a 15 second blast ofcooling air to reduce the specimen to a temperature of 1000 F. Theentire cooling and heating cycle took approximately 30 seconds. Thusvirtually the whole test period was spent at temperature. Weight anddimensional changes as shown in the above tables, as well asmetallographic examination were used to determine the amount ofoxidation. The following tensile properties of the alloy of the presentinvention particularly as represented by Example 1 were obtained on 60mil sheet.

TABLE VL-AVERAGE TENSILE PROPERTIES Temp. Ultimate 0.2 percent 0.2percent Percent F.) Tensile, Yield, Yield, Elong.

K s.i. K s.i. K s.i.

TABLE IV.-DYNAI\1IC OXIDATION TESTING IN FLAME TUNNEL 1,800 11, hours2,000" F., hours Example The data of Table IV shows that the alloy ofthe present invention experiences a significantly lower weight loss thandoes either Examples A or B. More significantly in connection with itsapplication as a useful article such as a combnstor in a gas turbineengine, the alloy of Example 1 has greatly improved resistance tointernal oxidation compared with Examples A and B. This is too difiicultto reduce from an ingot. The particular combination of lanthanum alongwith controlled amounts of such effective spinel forms as manganese andcobalt in the type of alloy to which this invention relates provides animproved alloy having oxidation resistance under dynamic conditionssignificantly better than those known prior to this invention as well asgood mechanical properties and good oxidation resistance under staticconditions.

Although the present invention has been described in connection withspecific examples such as of the effective spinel formers, it will berecognized by those skilled in the art other modifications andvariations of this invention can exist. It is intended by the appendedclaims to cover such variations and modifications.

What is claimed is:

1. An improved nickel base alloy of the solution strengthened typeconsisting essentially of, by weight, 20-23% Cr; 8-10% Mo; 17-20% Fe; upto about 0.15% C; up to about 2% W; 0.05 to less than 0.3% La; 0.5-6% ofthe spinel forming elements selected from the group consisting of Co andMn, the C0 when selected being in the range of 1-3% and the Mn whenselected being in the range 0.5-3%; with the balance nickel andincidental impurities.

2. An improved nickel base alloy of the solution strengthened typeconsisting essentially of, by weight, 20-23% Cr; 8-10% Mo; 17-20% Fe; upto about 0.15% C; up to about 2% W; 0.05 to less than 0.3% La; 1-3% Co;0.05-3% Mn; up to about 1% Si; with the balance nickel and incidentalimpurities.

3. An improved nickel base alloy of the solution strengthened typeconsisting essentially of, by weight, 20-23% Cr; 8-10%{Mo; 17-20% Fe;0.05-0.15% C;

6 up to about 2% W; 0.1-0.2% La; 1.5-2.5% Co; 0.5-1.5% Mn; up to about1% Si; with the balance nickel and incidental impurities.

4. An article including an alloy consisting essentially of, by weight,20-23% Cr; 8-10% Mo; 17-20% Fe; up to about 0.15% C; up to about 2% W;0.05 to less than 0.3% La; 0.5-6% of the spinel forming elementsselected from the group consisting of Co and Mn, the Co when selectedbeing in the range of 1-3% and the Mn when selected being in the rangeof 0.5-3%; with the balance nickel and incidental impurities; the alloyhaving a surface bonded with the alloy and comprising an integralcombination of Cr and La oxides and a spinel of the Ni( Cr, Mn, Co) Otype.

5. A combustion means for a gas turbine engine, the means including analloy consisting essentially of, by weight, 20-23% Cr; 8-10% Mo; 17-20%Fe; up to about 0.15% C; up to about 2% W; 0.05 to less than 0.3% La;l-3% Co; 0.05-3% Mn; up to about 1% Si; with the balance nickel andincidental impurities; the alloy having a surface bonded with the alloyand comprising an integral combination of Cr and La oxides and a spinelof the Ni(Cr, Mn, Co) O type.

References Cited UNITED STATES PATENTS 2,703,277 3/1955 Spendelow et a1.-171 3,304,176 2/1967 Wlodek 75-171 3,304,177 2/1967 Wlodek 75-171HYLAND BIZOT, Primary Examiner.

RICHARD O. DEAN, Examiner.

1. AN IMPROVED NICKEL BASE ALLOY OF THE SOLUTION STRENGTHENED TYPECONSISTING ESSENTIALLY OF, BE WEIGHT, 20-23% CR; 8-10% MO; 17-20% FE; UPTO ABOUT 0.15% C; UP TO ABOUT 2% W; 0.05 TO LESS THAN 0.3% LA; 0.5-6% OFTHE SPINEL FORMING ELEMENTS SELECTED FROM THE GROUP CONSISTING OF CO ANDMN, THE CO WHEN SELECTED BEING IN THE RANGE OF 1-3% AND THE MN WHENSELECTED BEING IN THE RANGE 0.5-3%; WITH THE BALANCE NICKEL ANDINCIDENTAL IMPURITIES.